Stent Delivery and Retention Apparatus

ABSTRACT

A stent delivery system comprises an inner member and an expandable balloon mounted in a collapsed state on the inner member, the expandable balloon having a first and a second end. A compressible stent having a first diameter is mounted in a compressed state around the expandable balloon between the first and second ends of the balloon. At least a first retainer pillow is formed in the expandable balloon at its first end and has an outer diameter which is at least substantially equal to the diameter of the compressed stent. A first pillow support member is mounted on the inner member and supports the first retainer pillow to maintain the pillow&#39;s outer diameter.

FIELD OF THE INVENTION

This invention relates generally to an intravascular stent deploymentapparatus, and more particularly to a stent delivery apparatus includingmarker bands which support distal and proximal pillows to providemechanical stent retention.

BACKGROUND OF THE INVENTION

In a typical percutaneous transluminal coronary angioplasty (PTCA)procedure, a guiding catheter is percutaneously introduced into thecardiovascular system of a patient. The guide catheter is advancedthrough a vessel until the distal end thereof is at desired location inthe vasculature. A guide wire and a dilatation catheter having a balloonon the distal end thereof are introduced into the guiding catheter withthe guidewire sliding through the dilatation catheter. The guide wire isfirst advanced out of the guiding catheter into the patient's coronaryvasculature, and the dilatation catheter is advanced over the previouslyadvanced guide wire until the dilatation balloon is properly positionedacross the lesion. Once in position, the flexible, expandable, preformedballoon is inflated to a predetermined size with a liquid or gas atrelatively high pressures (e.g. about ten to twelve atmospheres) toradially compress the arthrosclerotic plaque in the lesion against theinside of the artery wall and thereby dilate the lumen of the artery.The balloon is then deflated to a small profile so that the dilatationcatheter may be withdrawn from the patient's vasculature and blood flowresumed through the dilated artery.

In angioplasty procedures of the kind described above, there may occur arestenosis of the artery; i.e., a re-narrowing of the treated coronaryartery which is related to the development of neo-intinmal hyperplasiathat occurs within the artery after it has been treated as describedabove. In a sense, restenosis is scar tissue that forms in response tomechanical intervention within a vascular structure. To preventrestenosis and strengthen the area, an intravascular prosthesisgenerally referred to as a stent can be implanted for maintainingvascular patency inside the artery at the lesion. The stent is thenexpanded to a larger diameter for placement or implantation in thevasculature. This is often accomplished by the balloon portion of thecatheter. The stent effectively overcomes the natural tendency of thevessel walls of some patients to close back down, thereby maintaining anormal flow of blood through the vessel that would not be possible ifthe stent was not in place.

A known expandable stent which is delivered on a balloon catheter may beconsidered to be a stainless steel cylinder having a number of openingsin its circumference resulting in a scaffolding when expanded. Thestainless steel cylinder is compressed onto the outside of anon-expanded balloon catheter which includes stent retainer rings ateach end of the stent to help maintain the stent on the balloon.Unfortunately, the limited amount of securment between the stent and theballoon is not always adequate to insure that the stent will properlystay in place while advancing the stent to and through a target lesion.Additionally, the outer surface of the delivery device is uneven becausethe stent generally extends outwardly beyond the balloon. Thus, thestent may contact a narrow vessel wall and be displaced while thecatheter negotiates a narrow vessel. Furthermore, during a coronaryintervention, the physician may have difficulty crossing the targetlesion. In such cases, it may be necessary to pull the stent deliverysystem back into the guide catheter. Such procedures can be riskybecause the stent may become caught on the edge of the guide catheter.

For example, the guide catheter is generally inserted through theabdominal aorta to a point just beyond the ostium, the location fromwhich the right coronary artery and the left main artery diverge.Blockages or lesions are present in smaller coronary vessels, andmedical practitioners may sometimes predilatate the target area as, forexample, by balloon angioplasty. Sometimes, however, predilatation isnot performed, and doctors proceed directly to a primary stentingprocedure. In such cases, there are occasions when the balloon/stentcatheter cannot be properly positioned within the target area due to theconstriction of the vessel and must be retracted back into the guidecatheter. Even when predilatation is performed, vascular spasms and/or areclosure of the vessel may occur rendering it difficult to properlyalign the balloon/stent likewise requiring retraction into the guidecatheter. It is during the retraction process that the stent can catchor impact the edge of the guide catheter causing it to be dislocated orotherwise damaged.

To mitigate this problem, balloon pillows have been utilized to providea smooth transition of the balloon/stent assembly back into the guidecatheter. Such balloons may be produced through a process of heating andcooling in, for example, Teflon sheaths which are stacked in a way toproduce a step in the collapsed balloon surface. Once such system isshown and described in U.S. Pat. No. 5,836,965 issued Nov. 17, 1998 andentitled “Stent Delivery and Deployment Method.” In this apparatus,pillows formed in the balloon at opposite ends of the stent assist andsecure the stent to the balloon and create a smooth transition betweenthe stent area and the distal and proximal surface of the deliverydevice. The balloons may be tapered or non-tapered. Additionally,conventional retainers may be attached over the balloon or placed withinthe balloons. Unfortunately, the balloon material is generally verypliable, and it has been found that when using such devices, the pillowsmay collapse under the pressure of insertion and/or retraction thusexposing the edge of the stent to potential impact on the edge of theguide catheter.

It should therefore be appreciated that it would be desirable to providea low profile stent delivery and deployment apparatus which may beconfigured to have a generally smooth outer surface so as to avoidcollisions between the stent and other obstructions such as the edge ofthe guide catheter.

SUMMARY OF THE INVENTION

According to an aspect of the invention, there is a provided a stentdelivery system comprising an inner member and an expandable balloonmounted in a collapsed state on the inner member, the expandable balloonhaving the first end and a second end. A compressible stent is mountedin a compressed state of a first diameter around the expandable balloonbetween the first and second ends. At least a first retainer pillow isformed in the expandable balloon at the first end and has an outerdiameter which is at least substantially equal to the diameter of thestent. A first pillow support member is mounted on the inner member andsupports the first retainer pillow to maintain its outer diameter.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are illustrative of particular embodiments of theinvention and therefore do not limit the scope of the invention, but arepresented to assist in providing a proper understanding. The drawingsare not to scale (unless so stated) and are intended for use inconjunction with the explanations in the following detaileddescriptions. The present invention will hereinafter be described inconjunction with the appended drawings, wherein like reference numeralsdenote like elements, and;

FIG. 1 is a longitudinal cross sectional view of an stent and balloonassembly utilizing marker band support devices in accordance with thepresent invention;

FIG. 2 is an enlarged view of the proximal marker band and pillowsupport assembly shown in FIG. 1;

FIG. 3 is an enlarged view of the distal marker band and pillow supportassembly shown in FIG. 1;

FIG. 4 is an enlarged view of a marker band and pillow support assemblyin accordance with a further embodiment of the present invention;

FIG. 5 is an enlarged view of a marker band and pillow support assemblyin accordance with a still further embodiment of the present invention;

FIG. 6 is an enlarged view of a marker band and pillow support assemblyin accordance with a still further embodiment of the present invention;

FIG. 7 is a front view of the marker band and pillow support assemblyshown in FIG. 6; and

FIG. 8 is an isometric view of the marker band and pillow supportassembly shown in FIG. 6.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENT

The following description is exemplary in nature and is not intended tolimit the scope, applicability, or configuration of the invention in anyway. Rather, the following description provides a convenientillustration for implementing an exemplary embodiment of the invention.Various changes to the described embodiments may be made in the functionand arrangement of the elements described herein without departing fromthe scope of the invention.

FIG. 1 is a longitudinal, cross-sectional view of a balloon/stentassembly embodying the principles of the present invention. Theballoon/stent assembly shown generally at 20 comprises a stent 22, aninner member or wire lumen 24 having a distal end 26 and a proximal end28, and distal and proximal radiopaque marker bands 30 and 32respectively which are positioned on inner member or wire lumen 24substantially adjacent to distal and proximal ends of stent 22. Stent 22may be of any form or configuration suitable for the intended purpose,and may comprise one or more stent segments depending on the size andconfiguration of the vessel to be treated. It will be recognized bythose skilled in the art that inner member or guide lumen 24 isconfigured for the insertion of a conventional guide wire (not shown)which will enable the stent/balloon assembly to be guided and positionedat a target location in the vessel to be treated.

Any conventional or modified balloon catheter device may be used such asa PTCA balloon catheter. An expandable balloon portion 34 is mounted oninner member 24 in a compressed or collapsed state beneath stent 22 andextending beyond the proximal and distal ends of stent 22. Balloon 34 isgenerally made of a pliable material such as polyethylene, polyethyleneterathalate, PEBAX (polyamide block copolymers and polyester blockcopolymers), polyvinyl chloride, polyolefin, nylon or the like. Thelength and the diameter of the balloon may be selected to accommodatethe particular configuration of the stent to be deployed. Stent 22 maybe constructed of any implantable material having good mechanicalstrength, such as stainless steel, titanium, tantalum, super-elasticnickel-titanium alloys, or high-strength thermoplastic polymers. Theoutside of the stent may be selectively plated with platinum or otherimplantable radiopaque substance to provide visibility duringfluoroscopy. The cross sectional shape and the finished stent 22 maybecircular, ellipsoidal, rectangular, hexagonal, square, or any otherdesired shape, although a circular or ellipsoidal cross section ispreferable. The length and width of stent 22 is generally determined toa large degree by the size of the vessel into which the stent will bedeployed. It must be of sufficient length to maintain its axialorientation without shifting under the hydraulics of blood flow, longenough to extend across a significant portion of the target area, and atthe same time not be unnecessarily long so as to result in theintroduction of an unnecessarily large amount of material into thevessel.

After stent selection, the stent 22 is compressed upon the outside ofballoon 34. An inner sheath (not shown) is placed over each end ofballoon 34 and an exterior sheath (also not shown), is placed over theends of the interior sheath so as to cover stent 22 and overlap with theinterior sheaths. The assembly is then pressurized by introducing air oran inert gas such as nitrogen through the lumen 24 into the interior ofballoon 34 so as to expand the balloon within the sheaths. The assemblyis then exposed to an elevated temperature while maintainingpressurization of the balloon. The pressure may be, for example,approximately 70 psi and the temperature approximately 150 degreesFahrenheit. Following heating, the balloon/stent assembly is allowed tocool within the sheaths, and this cooling sets the shape of balloon 34.The sheaths may then be removed. Depending on the relative positioningof the inner and outer sheaths and stent 22 during the pressurizing,heating, and cooling process, there will be formed distal and proximalretainers or pillows 36 and 38 respectively which are intended to securestent 22 in position around balloon 34 and provide a smooth transitionbetween the balloon/stent portion of the delivery device and the distaland proximal ends of the delivery device.

Marker bands which may be viewed through fluoroscopy assist inpositioning the assembly. When the assembly is properly located across alesion, the balloon may be inflated in a conventional manner. Thisresults in the general uniform, symmetrical expansion of the stent andballoon. The amount of inflation and thus the amount of expansion of thestent may be varied as dictated by the lesion itself. The process bywhich retainers or pillows 36 and 38 are formed is described in detailin U.S. Pat. No. 5,836,965 entitled “Stent Delivery and DeploymentMethod” issued Nov. 17, 1998, the teachings of which are herebyincorporated by reference.

As stated previously, there are occasions when the balloon/stentcatheter cannot be properly positioned within the target area due to theconstriction of the vessel and therefore must be retracted back into theguide catheter. During this retraction process, the edge of the stentmight catch or impact the edge of the guide catheter causing it to bedislocated or otherwise damaged. Pillow 38 has an outer diameter whichis equal to or greater than the outer diameter of stent 22 and thereforeassists in providing a smooth transition between balloon 34 and stent 22as it is retracted. Furthermore, the lesion may be heavily calcifiedrequiring a higher insertion pressure. In this case, balloon 36 havingan outer diameter which is at least equal to the outer diameter of stent22 likewise represents an effort to provide a smooth transition betweenballoon 34 and stent 22 at the distal edge of stent 22. Unfortunately,as already mentioned, the balloon material is generally very pliable andas a result, pillows 38 and/or 34 may collapse thereby exposing theproximal edge of stent 22 during retraction and/or the distal edge ofstent 22 during insertion.

To prevent collapse of pillows 36 and 38, marker bands 32 and 30 areprovided with regions of higher diameter for supporting pillows 38 and36 as is shown in more detail in FIG. 2 and FIG. 3 respectively. Thus,the marker bands not only assist in the proper positioning of the stentwithin the target lesion, but also support the retainer pillows duringthe insertion and/or retraction process.

Referring to FIG. 2, there is shown a marker band or pillow supportmember 32 which includes a first region 40 having an inner diametersufficiently large to be frictionally or adhesively coupled on the innermember or wire lumen 24. The distal end of pillow support member 32includes a section 42 which is fixedly coupled to section 40 and has anouter diameter which approximates the outer diameter of stent 22 so asto maintain the pillow diameter at least equal to or greater than theouter diameter of stent 22. That is, section 42 supports pillow 38 insuch a manner as to maintain its outer diameter equal to or greater thanthe outer diameter of stent 22 so as to prevent the collapse of pillow38 and thereby provide a smooth transition should it be necessary toretract the stent/balloon assembly be back into the guide catheter.

In a similar manner, marker band or pillow support member 30, shown inFIG. 3, includes a first or distal section 44 having an outer diameterwhich is just sufficient to be mounted on inner member or wire lumen 24and to be retained thereon. Support member 30 includes a proximalsection 46 which is fixedly coupled to or formed integrally with section44 and has an outer diameter which is larger than that of section 44 soas to maintain the outer diameter of pillow 36 at least equal to theouter diameter of stent 22. In this manner, pillow 36 is prevented fromcollapsing should additional pressure be required to insert thestent/balloon assembly into a target lesion which is highly calcified.

In the embodiment shown in FIGS. 1, 2, and 3, pillow support members 30and 32 are coiled, spring like members which are mounted on inner member24 as described above and are preferably made of a memory alloy such asnitinol (nickel titanium). Thus, marker bands or pillow support members30 and 32 may be distorted as, for example, during the insertion orretraction process and still spring back to their original shape. Ofcourse, if the proximal and distal support members are not subjected tosignificant distortion forces, metals such as stainless steel, tungsten,and the like may be used.

It should be appreciated that marker bands 30 and 32 may be of anygeometry which offers the required pillow support so as to maintain theouter diameter of the pillows equal to or greater than the outerdiameter of the stent. For example, referring to FIG. 4, there is showna tapered marker band or pillow support member 48 which has an outerdiameter only slightly larger than the diameter of inner member 24 atits proximal end and tapers to a larger diameter at its distal endadjacent the edge of stent 22 so as to maintain the outer diameter ofpillow 38 substantially equal to or greater than the outer diameter ofstent 22. As was the case with the coiled marker bands shown in FIGS. 1,2, and 3, marker band 48 is made of a radiopaque substance so as to bevisible with low level X-rays thus assisting in the positioning of stent22 within the target lesion.

FIG. 5 illustrates another embodiment of the pillow support member inaccordance with the teachings of the present invention. In thisembodiment, a solid tubular marker band section 50 (e.g. a section oftubing having a length of, for example, one millimeter and made ofplatinum iridium or the like) has an outer diameter which is sufficientto permit section 50 to be positioned and retained on inner member orguide lumen 24. Another section 52 is fixedly coupled to or integrallyformed with the distal end of marker band tube 50 adjacent to theproximal end of stent 22 and has an outer diameter greater than theouter diameter of section 50 so as to support pillow 38. The outerdiameter of section 52 is large enough to maintain the outer diameter ofpillow 38 at least equal to or greater than the outer diameter of stent22. While support section 52 is shown as comprising a coil as was thecase in the embodiment shown in FIGS. 1, 2, and 3, it should beappreciated that support section 52 may be solid or take on any otherconfiguration which provides the necessary support to pillow 38.

FIG. 6 illustrates a still further embodiment of the present invention.In this case, a marker band and pillow support member shown generally at54 includes a central tubular member 56 (e.g., of the type shown in FIG.5) which has an outer diameter which permits it to be positioned andheld on inner member or wire lumen 24. A plurality of leaf springs 58are fixedly coupled to, as for example by brazing or welding, theproximal end of tubular member 56. Leaf spring members 58 terminate atcoil or ring 60 and are fixedly coupled thereto. The marker band/pillowsupport member 54 in accordance with this embodiment is shown in moredetail in FIGS. 7 and 8 which are front and isometric views. Leafsprings 58 are made of a memory alloy which may be deflected ordistorted and spring back to their original shape. Thus, ring 60 mayfloat when subjected to significant distortion and still return to itsoriginal position so as to maintain the outer diameter of pillow 38equal to or greater than the outer diameter of stent 22.

Thus, there has been provided an intravascular support device whichincludes radiopaque marker bands to assist in proper positioning of thedevice and which also support pillows 36 and 38 so as to assure a smoothtransition between stent 22 and pillows 36 and 38 when the device isbeing inserted into a target lesion or extracted back into the guidecatheter. While the primary application for the device is presently inthe treatment of cardiovascular disease such as atherosclerosis or otherforms of coronary narrowing, the device may also be used in thetreatment of vessels elsewhere in the body such as the kidney, leg, etc.It should be clear that in such cases, the size of the stent would beadjusted to accommodate the different sizes of vessels being treated.

In the foregoing specification, the invention has been described withreference to specific embodiments. It should be appreciated, however,that various modifications and changes might be made without departingfrom the scope of the invention as set forth in the appended claims.Accordingly, the specification and figures should be regarded asillustrative rather than restrictive, and all such modifications areintended to be included within the scope of the present invention.

1-6. (canceled)
 7. A stent delivery system according to claim 1 wherein said first support member is a tapered member which engages said inner member, and has a proximal diameter which tapers to a larger distal diameter.
 8. A stent delivery system according to claim 1 wherein said first support member includes a proximal tubular section of a second diameter which engages said inner member, and a distal coiled section of a third diameter for supporting said at least a first retainer pillow.
 9. A stent delivery system according to claim 8 wherein said distal coiled section is made of memory alloy.
 10. A stent delivery system according to claim 1 wherein said first support member includes a tubular section of a second diameter which engages inner member, and distal ring member of a third diameter resiliently coupled to said tubular section for supporting said at least a first retainer pillow.
 11. A stent delivery system according to claim 10 wherein said tubular section is coupled to said distal ring by a plurality of leaf springs.
 12. A stent delivery system according to claim 11 wherein said plurality of leaf springs are made of a memory alloy. 